So, think of your Facebook page as Stuart Smiley's mirror: It contains a lot of your core beliefs and preferences, and it puts your network of friends and family at your reach. In psychologist language, it can "satisfy fundamental ego needs regarding desired self-images."

You can't directly measure any Facebook bump in self-esteem or any bump generated other ways. But you can measure defensive behavior to criticism. It's been shown that the self-affirmation experiences similar to those spoofed by Stuart Smiley reduce defensive responses that are naturally elicited by ego threats.

Psychologists have tested this repeatedly. Usually they ask a participant to list strongly held beliefs and write an essay about the top one. After that, the participant invariably reacts better to a blow against the ego. The essay acts as self-affirmation.

The participant who chooses to write about a lower-ranked value but about how others may think it's important generally is more defensive. The essay had no self-affirming effect.

Turns out, looking at your own Facebook page is the social network equivalent of that first essay. Looking at another person's page is the non-affirming experience.

Catalina Toma, at the University of Wisconsin, and Jeffrey Hancock, at Cornell, study communication and social networks. They devised two experiments. In the first, some students got to look at their own Facebook page, while others looked at a stranger's page (it turned out to be another study participant's page). Some wrote the self-affirming essay, while others wrote the more neutral one.

Now the ruse: Participants were told they were there to evaluate a distance-learning public speaking course. Each was to write a short speech on the legality of abortion and deliver it to a camera, then get feedback and rate the feedback by various aspects. The trick: Participants wound up with the same negative feedback.

What happened? Results were as expected: less defensive response from people exposed to self-affirmation activity; more from those who did not get that experience. And it turned out that the proportion between those two responses was the same for those who wrote the essays as for those who viewed Facebook pages.

“Facebook has just as big an effect on self-esteem as traditional tools,” Hancock said.

But would someone who gets a negative feedback actively seek solace in Facebook? The second experiment tested that. They used a similar cover story: testing a public speaking program. But this time feedback was randomly negative or neutral. After the feedback, participants were allowed to choose an activity: looking at their own Facebook page, watching YouTube videos, listening to online music, reading online news or playing online video games.

After receiving neutral feedback, participants were equally likely to choose any of those activities. About 30% chose Facebook. But nearly twice as many chose Facebook after negative feedback.

Well, maybe more people prefer Facebook over the other activities, right? Researchers took that into account.

Facebook's rank among the activity choices (tested before the experiment) for those who got negative feedback was lower than the average rating of the other activities.

Why would any of this be important? Well, it gives experimenters a new tool to use instead of the essay, and there are about a billion people who use Facebook in any given month. That's a gigantic laboratory.

But Facebook might one day be part of therapies that use self-affirmation, such as programs to quit smoking or to change other habits.

“Anything you need to be stronger at, self-affirmation is good for you,” Hancock said.

Going in for a work evaluation anytime soon? Hancock advises: “Doing a little bit of Facebook before may be helpful.”